1. Field of the Invention
The present invention relates to a transmission apparatus, an access point and a symbol transmission method. More particularly, it relates to a transmission apparatus, an access point and a symbol transmission method of high data retransmission efficiency in a MIMO-OFDM communication system which employs a cyclic delay diversity.
2. Description of the Related Art
An orthogonal frequency division multiplexing (OFDM) mobile communication system is a transmission scheme which has excellent characteristics in a broad bandwidth, a frequency utilization efficiency and a radio propagation withstand characteristic. Further, there is a multiple input and multiple output (MIMO)-OFDM transmission scheme wherein transmission signals are spatially multiplexed with transmission antennas and reception antennas in the OFDM, thereby to realize the enhancement of a transmission rate.
Also, as a transmission diversity scheme for error-correction-coded OFDM signals, there is a scheme wherein OFDM signals after an inverse Fourier transform or after a cyclic delay diversity in which individual transmission symbols are transmitted by performing cyclic delays different between the respectively adjacent antennas are time-shifted and are thereafter transmitted by inserting cyclic prefixes (CPs).
The signals which do not correlate between the respective antennas are transmitted by applying this scheme to the MIMO-OFDM transmission scheme, so that the transmission rate can be raised in proportion to the transmission antennas.
On the other hand, in transmitting broadcast data, there have been disclosed methods wherein the data is efficiently transmitted by employing the cyclic delay diversity (refer to, for example, Patent Document 1 being JP-A-2005-354708). Incidentally, the MIMO-OFDM transmission scheme has been adopted as the transmission scheme of next-generation mobile communications.